Which option describes a similarity and a difference between isotopes of an element?
a) same atomic number; different number of protons
b) same number of protons; different atomic number
c) same atomic number; different mass number
d) same mass number; different atomic number
e) same number of neutrons; same number of protons

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.